Conventionally, an image reading device that reads an image that is an object to be read is known (refer to Patent Literature 1, for example). The image reading device described in Patent Literature 1 includes a cover glass on which the object to be read is placed. A light source element, and a light guiding body that irradiates a light emitted from the light source element onto the object to be read, are disposed on the side below the cover glass. Also, an imaging optical system and a sensor IC are arranged under the cover glass. With this image reading device, an image of a lower surface of the object to be read that is placed on the cover glass is read.